1. Field of the Invention
This invention relates particularly to an ignition apparatus based on semiconductors for determining an angular advance of an ignition position by an electronic circuit.
2. Description of the Prior Art
FIG. 1 is a circuit diagram illustrating a conventional ignition apparatus of the type referred to. As shown in FIG. 1, a magnetic rotor 1 is rotated in synchronism with an engine (not shown) and has a protrusion on one portion thereof; a pulser 2 which is composed of a magneto generator for detecting an ignition position of a maximum angular advance is provided; a similar pulser 3 is also provided for detecting an ignition position of a minimum angular advance.
A signal from the pulser 2 is arranged to be applied, as a setting signal, to a setting input S of RS FLIP-FLOP circuit 4 (which is called hereinafter a FF) and a signal from the pulser 3 is arranged to be applied, as a resetting signal, to a resetting input R of the FF 4.
An output Q of this FF 4 is connected through a resistance 5 to an inverting input of an operational amplifier 6 (which is called hereinafter an op-amp) and is also connected to an emitter of a transistor 9. An output end Q of the FF 4 is connected to a base of the transistor 9 through a pulse circuit 8.
This pulse circuit 8 may be a differentiation circuit for generating a pulse with a sufficiently short pulse width during the time that an output signal developed at the output Q of the FF 4 rises from an "L" level to an "H" level.
A non-inverting input of said op-amp 6 is supplied with a second voltage V.sub.2 and an output of this op-amp 6 is connected to a collector of the transistor 9 and is also connected to one input of a comparator 10. The other input of this comparator 10 is supplied with a first voltage V.sub.1. An integrating capacitor 7 is connected between the emitter and collector of the transistor 9.
The following description will be made by using timing charts of FIG. 2 (DIAGRAMS A-G) with respect to the operation of the ignition apparatus of FIG. 1. The waveforms shown by FIG. 2 (DIAGRAMS A-G) expresses signals on those portions shown by (a) to (g) in FIG. 1. A signal shown in FIG. 2(a) is outputted from the pulser 2 and on the other hand a signal shown in FIG. 2(b) is outputted from the pulser 3. Accordingly an output from the output Q of the FF 4 and the output from the output Q are substantially as shown in FIGS. 2(c) and (d) respectively.
First the FF 4 is put in its set state with a signal from the pulser 2 which has detected a maximum ignition advanced position and a discharging circuit is formed of the output Q of the FF 4, the resistance 5, the capacitor 7 and the output of the op-amp 6 to initiate the discharging of the capacitor 7 with a predetermined constant current. That is, the discharge current I.sub.1 results in ##EQU1## where V.sub.OH : Output voltage at its high level from RS FLIP-FLOP 4.
R.sub.5 : Magnitude of resistance of the resistance 5.
Then, when a signal detecting a minimum ignition advanced position is issued from the pulser 3, the FF 4 is inverted from its set state to its reset state to invert the output from the output Q of the FF 4 from its "L" level to its "H" level. Thus, an output is issued from the pulse circuit 8 as shown in FIG. 2(e).
The transistor 9 receives this output to cause the conduction thereof, causing the capacitor 7 to be shortcircuited. This capacitor 7 is rapidly discharged and the output voltage from the op-amp 6 becomes a set voltage at the non-inverting input thereof, that is, the second voltage V.sub.2. If the output signal from the pulse circuit 8 disappears, then the transistor 9 is cut off. Since the FF 4 has already been in its reset state, a charging circuit is formed which is the output of the op-amp 6, the capacitor 7, the resistance 5 and the output Q of the FF 4. The capacitor 7 is then charged with a predetermined constant current. That is, a charging current I.sub.2 results in ##EQU2## where V.sub.OL : output voltage at its low level from RS FLIP-FLOP 4.
Thereafter, the similar operation is repeated to depict a waveform as shown in FIG. 2(f) by the output voltage from the op-amp 6.
The comparator 10 compares the output voltage from said op-amp 6 with a first voltage V.sub.1 to generate a signal at a time point when the discharge voltage on the capacitor 7 is equal to said first voltage V.sub.1. Thereafter, it is operated so that a high voltage is generated on the secondary side of an ignition coil connected to a semiconductor switch (not shown).
At that time, assuming that the rotational speed of the engine is of N(RPM), and the spacing ratios of the maximum ignition advanced position and the minimum ignition advanced position are K.sub.1 and K.sub.2, and a period is T seconds, and the time interval from an ignition advance pulse position (FIG. 2(g)) to the minimum ignition advanced position is t seconds and the capacity of the capacitor 7 is C farads, then: ##EQU3## results by using the peak voltage V.sub.p on the capacitor 7.
From these two expressions (A) and (B) ##EQU4## results.
The conversion of this time interval of t seconds into an ignition advanced angle .THETA. results in ##EQU5## and it is understood that the ignition position advances rectilinearly in accordance with the rotational speed of the engine. When the rotational speed of the engine is smaller than a certain amounts, the voltage across the capacitor 7 becomes higher than V.sub.1 at a time point where the discharge is completed and the ignition advance pulse is issued upon the rapid discharge. In short, the minimum ignition advanced position becomes the ignition position.
The rotational speed with which the ignition advance is initiated is when the voltage across the capacitor 7, at a time point where the discharge is complete, may equal to the first voltage V.sub.1. This is be freely set by adjusting the first voltage V.sub.1, the second voltage V.sub.2, the capacity of the capacitor 7, the magnitude of the resistance 5, etc. Also, if the rotational speed of the engine is larger than a certain amount, then the peak V.sub.P of the voltage across the capacitor 7 at a time point where the charge is completed becomes less than V.sub.1 and the ignition advance pulse from the comparator 10 is not obtained. In a region of this rotational speed, the maximum ignition advanced position from the pulser 2 makes an ignition position although it is not illustrated.
The rotational speed with which the ignition advance terminates is when V.sub.2 =V.sub.1. This can be freely set by adjusting the first voltage V.sub.1, the second voltage V.sub.2, the charging current I.sub.2, the capacity of the capacitor 7, etc. Also, the minimum ignition advanced position and the maximum ignition advanced position can be freely set by changing the positions of the pulsers 2 and 3.
Since the conventional ignition apparatus is constructed as described above, it is possible to control the ignition advance so as to be proportional to the rotational speed of the engine, but it has not been possible to control the ignition advance in dependence upon the status of the engine, for example, a temperature or a vacuum in a manifold. Thus, there has been the disadvantage in that the ignition advance characteristic required for the engine is not sufficiently adjusted.
Also, as an apparatus of the type referred to, there has previously existed what is illustrated in Japanese laid-open patent application No. 96,365/1980. According to said well-known example, a first triangular wave generator means is required for generating a reference voltage rising with a predetermined tilted angle from an ignition position of a minimum ignition advance to an ignition position of a maximum ignition advance, and flat after the ignition advance and inversely proportional to the rotational speed of the engine, and a third triangular wave generator means is required for generating a voltage rising from the ignition position of the maximum ignition advance with a predetermined tilted angle according with to the status of the engine, and a second triangular wave generator means is required for setting an ignition advance, by generating a voltage rising from an intersection of the reference voltage inversely proportional to the rotational speed according to said first triangular wave generator means and said third triangular wave voltage. The first, second and third triangular wave generator means have respectively required separate integrating capacitors. Thus, the ignition advance characteristic includes capacities of the three capacitors in its variables so that there have been the disadvantages in that the initial adjustment of the ignition advance characteristic is complicated and the ignition advance characteristic is easily varied with ageing changes in the capacities of the capacitors. Furthermore, there have also been disadvantages in that the integrating capacitor may normally require a high capacity and the hybrid integration thereof is difficult, thereby limiting the possibility rendering the apparatus small sized and cheap.
Also, the ignition advanced angle has been able to be controlled by changing a tilted angle of the third triangular wave in accordance with the status of the engine without relying on the rotational speed of the engine. However, a rectilinearly proportional relationship does not exist between amounts of the changes in tilt of said triangular wave voltages and the controlled ignition advanced angle so that, for example, where an output signal from a vacuum sensor which has been rectilinarly changed in accordance with a vacuum in the engine so as to control the ignition advanced angle in proportion to a magnitude of the vacuum, there has been the disadvantage in that an interface circuit between the vacuum sensor and a circuit for controlling the tilt of the third triangular wave voltage is complicated.